Asphaltenes are one of the four main constituents of crude oil, which also include saturates, aromatics, and resins. Asphaltenes impact virtually all aspects of the utilization of crude oils, and mostly have negative effects. For example, asphaltenes precipitation or deposition can occur in wellbores, pipelines, and surface facilities and is undesirable because it reduces well productivity and limits fluid flow. For refiners, asphaltenes cause concern because they can clog the refining system. Due to presence of sulfur, nitrogen and metals in the structures, asphaltenes can cause rapid catalyst deactivation during catalytic processing of crude oils. Therefore, asphaltenes are a cause of major economic, technical and safety problems during the production and processing of crude oils.
Given the operational problems caused by the presence of asphaltenes, separation of asphaltenes and other heavy species from crude oil is desirable. Solutions to address the operational problems of asphaltenes must address both problems of asphaltenes precipitation. And these solutions must improve the crude oil specifications including raising API gravity and decreasing crude oil viscosity. The API gravity and viscosity impact the price of crude oil.
One solution that addresses asphaltenes precipitation is the use of anti-scaling agents. Anti-scaling agents have been tested by researchers as a way to stabilize the asphaltenes suspensions in the crude oil, and by stabilizing the asphaltenes prevents precipitation during crude oil transportation and refining. However, asphaltenes decompose at high temperatures even with the use of anti-scaling agents, which can cause coke formation in heat exchanger and furnaces.
Another solution is hydrotreating the crude oil. Hydrotreating is a process that uses hydrogen to convert compounds in the crude oil. Hydrotreating requires high temperatures and high pressures which results in a process that is energy intensive. In addition, hydrotreating requires expensive catalyst. The use of hydrogen poses a risk of hydrogen explosion. Finally, tail gas from a hydrotreater cannot be directly released to the atmosphere, requiring some type of tail gas exhaust treatment.
Conventional asphaltene separation technology, generally referred to as solvent de-asphalting (SDA), involves the application of paraffinic solvents. SDA processes are based on liquid-liquid extraction using paraffinic solvents. SDA technology is considered one of the most efficient approaches to reduce asphaltenes and metal content of crude oil and heavy oil cuts to produce higher-value de-asphalted oil (DAO). SDA processes offer the advantages of low installation cost and flexibility in terms of the ability to control the quality of asphaltenes and DAO. However, the SDA process requires a considerable amount of expensive paraffinic solvents (the paraffinic solvent to crude oil ratio is typically from 2:1 to 10:1 by volume). The paraffinic solvent type directly decides the yield and quality of DAO; as the carbon number of the paraffinic solvent increases, the yield of recovered DAO will increase, but the quality of DAO will be reduced. Furthermore, the separation and recovery of paraffinic solvents from DAO are energy-intensive processes. Solvent recovery through a distillation process is not possible due to the wide range of boiling points of crude oil components, so a more complex solvent recovery technique, such as single-effect evaporation, double-effect evaporation, or triple-effect evaporation is needed. The large amount of waste paraffinic solvents is also another drawback of SDA.